A post on the HL2world
Forums outlines the fairly simple method for getting a Half-Life 2
deathmatch server (as opposed to Counter-Strike Source) running (thanks
sauron). This is unsupported and certain aspects of this are a bit wonky,
for instance, there doesn't seem to be a Gordon Freeman model for this purpose.
Here is the sequence of console commands they've worked out:

Sorry, I'm not interested in your immature, fashionable euphuisms. Unless I were a little teenie like yourself I would have no idea what that statement means as it lacks meaning. It makes you sound like a pathetic follower of others & shows your utter lack of leadership. When I was a little kid like yourself, I didn't resort to the stupid blather that the other kids took part in. I bet you have a pierced tongue & dickhead so you can try to please Goatsee. But hey, at least your fashionable. Right? DUMBASS!